Introduction

The Olive Sparrow is a retiring inhabitant of dense thorn-scrub in southern Texas and the coastal plains of Mexico and northern Central America, spending most of its life on or near the ground in dense cover. Most often heard singing its “metallic bouncing ball” song or giving its dry tsip note, the Olive Sparrow only occasionally forages in the open. Because of its retiring habits, little is known of this species’ breeding biology, behavior, or feeding habits. Its partially domed nest is usually placed on or near the ground under dense cover, but the exact incubation period and nestling period remain unknown.

The Olive Sparrow is one of a small group of sedentary, tropical Arremonops sparrows that occurs from southern Texas to northern South America. Nine subspecies of Olive Sparrow have been recognized; these differ in relative lengths of tail and wings, bill size and color, and the colors of under-parts and head-stripes. Populations in eastern and western Mexico, northwestern Costa Rica, northern Guatemala, and the Yucatan Peninsula are disjunct, and some may be distinguishable at the species level. Although heavily parasitized by Bronzed Cowbirds (Molothrus aeneus) in southern Texas, the Olive Sparrow is a common resident of semiarid subtropical areas where appropriate habitat remains. Since it inhabits subtropical and tropical areas varying in precipitation and annual temperature range, this Sparrow would be an appropriate species in which to study variation in clutch size and survival.